Children's ability to use a literate oral language style, consisting of precise vocabulary and elaborated grammatical structures, is an important foundation for reading readiness and school success. Previous research has focused on the contribution of parent language input to individual differences in children's vocabulary growth. However, much less is known about the contribution of parent language input to individual differences in young children's grammatical development, creating an empirical barrier to the further development of cost-effective early grammatical interventions. In previous research, we have demonstrated that significant individual differences in children's productive use of tense and agreement appear between 21 and 30 months of age (Hadley & Holt, 2006; Rispoli, Hadley, & Holt, 2009), and we have also identified abstract grammatical properties of parents' language input to their 21-month-old toddlers that contribute to the observed between-child differences (Hadley, Rispoli, Fitzgerald, & Bahnsen, in press). The proposed project builds upon our prior success modeling grammatical growth in children under age 3, investigating biological, developmental, and input predictors of grammatical growth, and understanding the way in which sentence diversity, language typology, and parent interaction style influence the grammatical richness of adult input. This project will develop and evaluate the effectiveness of new psycholinguistically-motivated language modeling strategies through a parent education intervention. Twenty-four toddler-parent dyads will be recruited. Parents will learn to talk about the actions, states, and properties of the toys their children are playing with and to use specific noun labels rather than pronouns (e.g., The nose fits, NOT It fits). This new strategy is referred to as toy talk. Parent input and children's grammatical growth will be compared to an existing no-treatment control group. The specific aims address: (a) whether parents in the toy talk intervention provide richer grammatical input in comparison to parents in the control group, and (b) whether such input modifications accelerate the grammatical development of children in the intervention group between 21 and 30 months of age. Because toy talk strategies are expected to increase the use of 3rd person lexical noun phrases (NP) in subject position, parents' overall input sentence diversity (i.e., unique subject-lexical verb combinations) and input informativeness for tense/agreement marking should also increase. We also hypothesize that the presence of lexical NP subjects in the adult input will strengthen children's abstract grammatical representation of the subject / predicate relation. This, in turn, is expected to support the integration of the clause level grammatical features of tense and subject-verb agreement into the representation, resulting in more rapid grammatical growth for children in the intervention group relative to the control group. If successful, this project will establish the centrality of sentence diversity to the development of tense and agreement and provide crucial theoretical information about how children make use of input in the acquisition of grammar.